1. Field of the Invention
The present invention relates to the field of digital broadcasting. More specifically, the present invention relates to distributed conditional access (CA) on a serial communication network which supports digital cable broadcast systems.
2. Related Art
Television (TV) programming and other kinds of broadcast services are commonly available to the public via subscription from the respective providers, such as cable TV and satellite TV service providers. A viewing subscription typically includes certain basic services, such as programming from local TV stations, that are provided as part of the basic subscription. Additionally, the subscription may also include pay-per-view (PPV) programs, where the customer decides to pay for and watch and/or record a program such as a movie or a sports event spontaneously, that are not covered by the basic subscription fee. In order to implement appropriate access restrictions on individual customers according to their subscriptions, the broadcast signals are scrambled or encrypted, and an electronic set top box (STB) with specific descrambling capabilities is supplied by the service providers to each of their customers. Using the STB, each customer can then access the programming that he/she has paid for in unscrambled form. In the broadcasting art, the selective descrambling of broadcast signals is commonly referred to as conditional access (CA) control and the programming and other services that require such descrambling by the service recipients (e.g., PPV programs) are often called CA services.
To implement conditional access control, different programming contents carried by broadcast signals are typically encrypted using different encryption schemes. For example, the programming content of a PPV movie channel is usually encrypted differently from that of a PPV sports channel, such that a separate decryption scheme--and thus a separate authorization for payment, for example--is required to gain access to the descrambled content of each PPV channel. On the other hand, an STB is typically equipped with a few slots, each of which can accept a physical card, e.g., a PCMCIA card or a smart card. Each electronic card enables the STB to descramble or decrypt the contents of a limited number of channels. Thus, by providing their customers with the appropriate card(s) in the STBs based on their individual subscriptions, the service providers can control the programming contents that each customer is able to access accordingly.
As thus described, the CA mechanism is built into each STB in the prior art. Consequently, the cost of implementing the CA technology, such as the cost of PCMCIA electronics and connectors and of smart card readers, are incurred for each STB irrespective of whether the particular customer wants to have CA services or not. In other words, a substantial number of prior art STBs include extraneous components that unnecessarily inflate the unit cost of STBs for the service providers. Moreover, for those customers who subscribe to CA services, additional costs are incurred for the corresponding PCMCIA and/or smart cards. It would be advantageous to reduce the cost of the STB by avoiding the costs associated with the electronic component and cards.
Just as importantly, the prior art CA mechanism inherently limits the number of CA services that can be consumed (e.g., watching, recording) at a given time. This is because a prior art card-based STB is physically limited in size and can only accommodate a fixed number of PCMCIA and/or smart cards (as limited by the number of card slots in the STB), and each card typically can only descramble one or two services at a given time. Thus, the prior art CA mechanism does not work well in an environment having a large number of CA services (e.g., numerous TV channels), as is typical in a digital broadcasting environment, since too many cards would be required to handle the different CA services.
Thus, as a result, not only is the prior art CA mechanism costly to implement (especially the PCMCIA solution), but it also precludes a customer from simultaneously accessing more CA services beyond the few that can be descrambled by the STB during any given period, even if additional programs are available from the service providers and the customer desires to purchase such PPV programs (e.g., to record several movies that are being broadcasted concurrently). Consequently, the flexibility with which a customer can purchase multiple CA services is greatly limited, since the customer's purchasing decision is constrained by the number of concurrent programs that the STB can support. At the same time, the potential revenue of the service providers is vastly limited because desired PPV purchases are often precluded by this technological limitation of the prior art STB. Therefore, it would be highly desirable to maximize the flexibility and parallel descrambling capability of the CA control by eliminating the inherent limitations of the card-based STB.
The advent of digital broadcast technology has enabled the use of a serial communication network for high speed and flexible interconnection of various devices and appliances within a network environment. The IEEE 1394 communication standard is a widely adopted serial communication network standard ("1394 network") in the art. For example, within a consumer household, personal computers (PCs), audio systems, STBs, TVs, video cassette recorders (VCRs) and other AV/C-compliant media devices can all be communicatively coupled together in a 1394 network. In such a network environment, the individual devices can interact with each other and facilitate the coordination of the different functionalities provided by the various devices.
With this technological backdrop, it has been proposed that the CA functionality for such a 1394 network be removed from the STBs (as is the case in the prior art STBs) and instead be implemented separately on the 1394 network. As such, the extraneous cost and limited descrambling capability problems inherent in the prior art, in which the CA functionality is built into the STBs, can potentially be resolved.
Nevertheless, an additional challenge exists with respect to the implementation of distributed CA functionality on a 1394 network. The problem posed relates to out-of-band (OOB) processing of digital broadcast signals. More particularly, within digital broadcast systems, some service providers deliver a scrambled broadcast signal (which encodes a CA service such as a PPV program) and its respective descrambling information in completely separate frequency ranges. Regular TV broadcast signals and the descrambling information for the regular broadcast signals (OOB data) are carried in separate frequency ranges. In this environment, not only is the prior art STB cost inefficient and limited in descrambling capability as described above, but its internal architecture is also ill-suited for simultaneous handling of the regular broadcast signal and the OOB data which are broadcasted in different frequencies. As such, the prior art STB design is not a viable option for implementing CA control on a 1394 network.